I'm using the "cinnamon" desktop theme with the Atlanta window-borders theme. Both of these ship with the OS version that I'm running, LMDE2 "Betsy" Cinnamon 64-bit.

When a panel is on the top edge of the screen, and a window is maximized, the panel + the window titlebar look totally flat, like one big window titlebar, especially if there aren't a lot of applets in the part of the panel where the user is looking:

Cinnamon panel & 2 window titlebars.png

This can result in the user beginning a mouse-drag, right-click, etc. on the panel when wanting to do so on the window titlebar instead.

Suggestion: Prefer adding a "bevel" which can be a color gradient, maybe 2px high, on the edge of the panel that's toward the center of the screen (the bottom edge of the panel in this case). I believe some other desktop environments have this in their (not always themable) panel equivalents. I mean this "bevel" suggestion as a guideline for desktop-theme developers, although it would be great if a few more of the desktop themes that ship with Cinnamon would have this change made.

I picked the desktop theme, rather than the window-borders theme, for this suggested guideline for the following reason: Desktop themes seem to be specific to Cinnamon, whereas window-border themes are used everywhere GTK+ is used, and often in DEs that already have a bevel on their panel, or don't put a panel @ top of screen at all, so a bigger percentage of desktop-theme developers would be willing to observe this guideline AOT window-border developers.
(AOT = as opposed to)

About my own desktop setup:

I chose the "cinnamon" desktop theme because sometimes I have a lot of windows open, and the buttons in the window-list applet fit the best (the most characters of text per button) with the "cinnamon" theme.

I chose the "Atlanta" window-borders theme because that has big window decorations (including the side & bottom borders) compared to other window-border themes.

My point there is that "just pick another desktop theme or window-borders theme from among those that ship with Cinnamon" may not be desirable.

Also, I think this is a basic enough issue that it would be nice to take care of it in the default themes, so the user doesn't have to begin to wade through spices for this purpose.

Edit: Changed the title to match another suggestion I want to make in this thread.

In the Panel, the window-list applet currently is like so (if panel is @ bottom of screen):

Button of non-focused window: A medium brownish-gray color from top to bottom.

Button of the focused window: The same, except a gradient in which the top of the button is light gray.

The text in both cases is white.

In my opinion, this isn't enough contrast between the buttons of the focused and non-focused windows, especially if there are only a couple of window buttons in the window list. In the latter case, I'm constantly clicking the wrong window button because the gradient doesn't communicate well enough which window is focused & which ones aren't.

It might be better if the button of the focused window were drawn in a way that contrasts more with buttons of non-focused windows. For instance, the background & text colors could be swapped (medium brownish-gray text on white background). This combination of colors happens to make the "focused" button look brighter overall, which should convey "focused." Or some variation on that graphical effect could be used.

Same disclaimers as in my previous posting: Yes, other themes are available and no, I don't expect anyone to change the "cinnamon" theme right away, but it would be nice if someday the themes included with the Cinnamon desktop were improved. I don't think my suggested changes are too radical.